The new facilities in Brooklyn and Manhattan would be located at the site of the jails that currently operate in those boroughs, adjacent to the local courthouses, Mayor Bill de Blasio and Corey Johnson, the City Council speaker, said Wednesday at a news conference.

In Queens, the city would use the site of the former jail near the courts in Kew Gardens. In the Bronx, de Blasio said he would locate a new jail at a Police Department tow pound parking lot in Mott Haven, about 2 miles from the criminal courthouse. The Council members who represent the districts where the new jails would be located have all endorsed the plan.

De Blasio said there would be no new jail in Staten Island.

After long resisting calls to close the Rikers Island complex, the mayor announced last March that he supported shuttering the remote facility, which is plagued by violence and other problems, but said that it would take 10 years.

On Wednesday, with prodding from Johnson, de Blasio said it might be possible to move more quickly.

“Ten years is too long,” Johnson said at a news conference in the City Hall rotunda. “I’ve been telling the mayor that, and the mayor agrees.”

The mayor later hedged on the timeline, in response to questions from reporters. “We want to go as fast as we can,” he said. “With what we know today, 10 years is the timeline.” He said that designing new jails, going through the land-use process to get approval and then building them was a lengthy undertaking.

The mayor said that the state government needs to take several steps to reduce the total jail population enough so that the relocation plan will be feasible. Those steps include passing laws to reform the bail system and making trials move faster. “If all that gets done then we can speed this timeline up by years,” de Blasio said.